One type of presently known brake cylinders, as is known to those skilled in the art, is spring-actuated for effecting a brake application and is provided with a release piston subject to the force of a spring for effecting a full or emergency brake application and is subjectable to an opposing fluid pressure force for effecting a release of the brakes by counteracting the spring force. Fluid pressure must be continuously maintained against the release piston, however, in order to keep the brakes released while the vehicle is in motion. The brake cylinder in question is also provided with a service application piston arranged in opposing relation to the release piston so that when the opposing pressure areas of both pistons are concurrently subjected to the aforementioned fluid pressure, such pressure acting on the release piston causes said release piston to be operated to a brake release position, whereas pressure acting on the service piston effects a service application according to the degree of force differential between the opposing forces.
In this situation, however, the spring force acting on the release piston is constantly present, so that the degree of fluid pressure counteracting such spring force for operating the release piston to a release position and for effecting a service application must be of a sufficient degree as to compensate for the spring force.